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Abstract

Monte Carlo (MC) simulations are frequently used to simulate the radial
distribution of remitted
fluorescence light from tissue
surfaces upon pencil beam excitation to gather information about influences of
different tissue parameters. Here, the “weighted direct emission
method” (WDEM) is proposed, which uses a weighted MC simulation approach
for both excitation and fluorescence photons, and is compared to four other
methods in terms of accuracy and speed, and using a broad range of
tissue-relevant optical parameters.
The WDEM is 5.2× faster on average than a fixed weight MC
approach while still preserving its accuracy. Additional gain of speed can be
achieved by implementing it on graphics
processing units.

References

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Overview of the Methods Used for the Different Simulation Methods

Table 2.

List of the Simulation Input Optical Parameters Denoted by aa to cc, with
Three Different Absorptiona,b
and Scattering
Coefficientsa,c,
Respectively

aa

ab

ac

ba

bb

bc

ca

cb

cc

LOW

μa,x

1.0

1.0

1.0

0.2

0.2

0.2

5.0

5.0

5.0

μa,m

0.5

0.5

0.5

0.1

0.1

0.1

2.5

2.5

2.5

μs,x

20

4

100

20

4

100

20

4

100

μs,m

15

3

75

15

3

75

15

3

75

HIGH

μa,x

1.0

1.0

1.0

0.2

0.2

0.2

5.0

5.0

5.0

μa,m

0.5

0.5

0.5

0.1

0.1

0.1

2.5

2.5

2.5

μs,x

200

40

1000

200

40

1000

200

40

1000

μs,m

150

30

750

150

30

750

150

30

750

a The subscript “x” denotes the excitation
wavelength, “m” the emission
wavelength.b The absorption coefficient at the excitation wavelength
μa,x includes both absorption by tissue
and fluorophore.c Low scattering coefficients (“LOW”), high scattering
coefficients (“HIGH”).

Table 3.

Total Remitted Fluorescence in Percent, Normalized to the Excitation Photons,
for the Five Different Methods for 18 Different Optical Parametersa Denoted by aa
to cc

Table 4.

Comparison of the Results for
the Different Methods

a The average speed for simulation of the remitted fluorescence light
distribution for 18 different sets of optical parameters, with
“++” indicating very fast and
“−−” very slow simulations.b The DEM and WDEM yield accurate results
(“+”), the FEM and RM suffer from
additional convolution imprecisions (“−”) compared to the WSEM
(“0”).

Tables (4)

Table 1.

Overview of the Methods Used for the Different Simulation Methods

Excitation

Fluorescence

Weighted Simulation

Weighted Simulation

Direct Emission

Convolution Necessary

DEM

no

no

yes

no

WDEM

yes

yes

yes

no

WSEM

yes

yes

no

no

FEM

yes

yes

no

yes

RM

yes

yes

no

yes

Table 2.

List of the Simulation Input Optical Parameters Denoted by aa to cc, with
Three Different Absorptiona,b
and Scattering
Coefficientsa,c,
Respectively

aa

ab

ac

ba

bb

bc

ca

cb

cc

LOW

μa,x

1.0

1.0

1.0

0.2

0.2

0.2

5.0

5.0

5.0

μa,m

0.5

0.5

0.5

0.1

0.1

0.1

2.5

2.5

2.5

μs,x

20

4

100

20

4

100

20

4

100

μs,m

15

3

75

15

3

75

15

3

75

HIGH

μa,x

1.0

1.0

1.0

0.2

0.2

0.2

5.0

5.0

5.0

μa,m

0.5

0.5

0.5

0.1

0.1

0.1

2.5

2.5

2.5

μs,x

200

40

1000

200

40

1000

200

40

1000

μs,m

150

30

750

150

30

750

150

30

750

a The subscript “x” denotes the excitation
wavelength, “m” the emission
wavelength.b The absorption coefficient at the excitation wavelength
μa,x includes both absorption by tissue
and fluorophore.c Low scattering coefficients (“LOW”), high scattering
coefficients (“HIGH”).

Table 3.

Total Remitted Fluorescence in Percent, Normalized to the Excitation Photons,
for the Five Different Methods for 18 Different Optical Parametersa Denoted by aa
to cc

Table 4.

a The average speed for simulation of the remitted fluorescence light
distribution for 18 different sets of optical parameters, with
“++” indicating very fast and
“−−” very slow simulations.b The DEM and WDEM yield accurate results
(“+”), the FEM and RM suffer from
additional convolution imprecisions (“−”) compared to the WSEM
(“0”).